The present invention relates to an electrophotographic recording material comprising an electrically conductive base material and at least one photoconductive layer containing an organic photoconductor, a binder, and one or more cyanine sensitizing dyes of a specific type, along with customary additives, if any.
In the field of electrophotographic reproduction, photoconductors are used that are radiation-sensitive into the short-wave visible portion of the spectrum. The radiation sensitivity of such photoconductors in the visible portion of the spectrum can be extended by adding one or more sensitizing dyes which are capable of transferring the energy of longer-wavelength light to the photoconductor. Sensitizing dyes from a very wide range of classes of compounds have been used for this purpose.
It is known (German Auslegeschrift No. 2,526,720, corresponding to U.S. Pat. No. 4,063,948) to use for electrophotographic reproduction an electrophotographic recording material that contains in the photoconductive layer a cyanine dye which has a sensitizing action in the blue part of the spectrum. However, such a sensitizing action does not make it possible to utilize the energy from light sources which, like incandescent lamps, have a high red content.
It is alwo known (European Patent Application No. 106,963) to use, as sensitizing dyes in zinc oxide photoconductor layers, special heptamethinecyanines having a betaine structure and a sensitivity within the spectral region between 780 and 840 nm. But these sensitizing dyes do not meet the highest requirements of reproduction. A very specific binder mixture of a styrene/acrylate resin and a vinyl alkanoate resin must also be used in preparing a layer which contains the dyes in question. Even combined with customary organic photoconductors, these sensitizing dyes provide an insufficient sensitizing action.
It is also known (German Offenlegungsschrift No. 1,447,907, corresponding to U.S. Pat. No. 3,458,310) to sensitize photoconductor layers to the visible red wavelengths. This is done, for example, by means of dye mixtures of acridine yellow, acridine orange, rhodamine and brilliant green which are added in one or separately in different layers (German Offenlegungsschrift No. 2,353,639, corresponding to U.S. Pat. No. 3,992,205). The action of the individual dyes being additive or, alternatively, the sensitization which occurs can be different from the summated sensitization spectrum of the individual dyes (German Offenlegungsschrift No. 2,817,428, corresponding to U.S. Pat. No. 4,252,880).
Such panchromatic sensitizations offer advantages, in that light sources with a high red content, which are used in reproduction technology, are utilized more efficiently. In practice, this means shorter exposure times and, hence, time and energy savings. It is possible, not least on accout on the improved sensitivities, to reduce the photoconductor content in the photoconductive layer. The disadvantage with such a continuous sensitization, however, is that the material cannot be processed in physiologically favorable, bright darkroom light.
Many dyes with a powerful sensitizing action in the red spectrum, such as those of the triphenylmethane dye series, effect a very broad sensitization which, nevertheless, has a maximum that generally does not go beyond 700 nm. For that reason, light sources which emit at longer wavelengths cannot be fully utilized, nor is it possible to process the material in bright darkroom light without damaging the material.